Lubricant for refrigerating machine employing ammonia refrigerant

ABSTRACT

A lubricant for a refrigerator using ammonia as the refrigerant, which contains an additive selected from antioxidant, anti-wear additive and metal deactivator, and the polyether compound represented by the following general formula (1) or (2):
 
X{—O—(AO) n —H} p   (1)
 
X{—O—(AO 1 ) a —(AO 2 ) b —H} p   (2)

TECHNICAL FIELD

The present invention relates to a lubricant for a refrigerator using anammonia refrigerant.

BACKGROUND ART

A compression refrigerator comprises a compressor, a condenser, anexpansion mechanism (for example, an expansion valve or a capillarytube), an evaporator and the like, and is an apparatus where a coolingis performed using a characteristic of a refrigerant having a highvolatility to take away an heat of evaporation from its surroundingsupon the evaporation. This apparatus is being used for vending machinessuch as a cooler, a freezer, an air conditioning equipment, a show case,soft drink, ice cream or the like. In the air conditioning equipment orthe vending machine, the compression refrigerator is being used also forperforming the heating or keeping a drink or a food under heating,utilizing a heat generated upon the condensation.

As the above-described refrigerant, a chlorine-containingfluorohydrocarbon (CFC or HCFC) is conventionally used, and it has beenreplace by a chlorine-free fluorohydrocarbon (HFC) in recent years.However, these fluorohydrocarbons have a problem that the formerdestroys the ozone layer and the latter has a high global warming effectand therefore, in place of these, such a refrigerant that exerts noadverse effect on the environment is being demanded from the viewpointof global environment protection. Accordingly, a refrigerant such ashydrocarbon or ammonia having a low molecular weight has beenreconsidered as an environment-friendly refrigerant because it does notdestroy the ozone layer and is extremely low in global warming effect ascompared with the fluorohydrocarbon. In particular, ammonia has a highperformance coefficient.

As a base oil of a lubricant for refrigerator using an ammoniarefrigerant, a mineral oil or alkylbenzene has been conventionally used.However, a polyether compound having compatibility with ammonia has beenproposed in recent years. For example, European Patent Publication490810 discloses a lubricant comprising a polyalkylene glycol which is acopolymer of ethylene oxide and propylene oxide and has an EO/PO ratioof 4/1. European Patent Publication 585934 discloses a lubricantcomprising a monofunctional or difunctional polyalkylene glycol havingan EO/PO ratio of 2/1 to 1/2. German Patent Publication 4404804discloses a polyether-base lubricant represented by the general formula:RO—(EO)_(x)—(PO)_(y)—H[wherein R represents C1 to C8 alkyl group, X and Y are numbers from 5to 55]. International Patent Publication WO 94/12594 discloses arefrigerator oil comprising a polyalkylene glycol diether, which isexcellent in the compatibility with ammonia and the stability in anammoniac atmosphere.

If these polyether compounds having the compatibility with ammonia areused, it is not necessary to provide a lubricant circulator where alubricant is separated and recovered at the exhaust side of arefrigerating compressor and returned to the compressor.

However, ammonia as a refrigerant is a compound having a high activity,and therefore there is a fear that the ammonia reacts with a base oil oran additive of a lubricant for refrigerator or with the deterioratedmaterial thereof to produce a precipitate (reaction product), whichcauses blocking of an expansion valve or a capillary portion and thewear of a sliding member, and also accelerate the deterioration of thelubricant. Ammonia has high corrosiveness with respect to a metalmaterial, particularly in the presence of water. Therefore, if ammoniais used together with a polyether compound having high moistureabsorption, the corrosion or deterioration of metal materials such asoccurrence of rust is accelerated. Further, since an ammonia refrigerantrequires a higher pressure driving than a flon-base refrigerant, therefrigerant and the lubricant are exposed to severer conditions such ashigh temperature and high pressure, and also severer sliding conditionsapply. As a result, the increase in the generation of precipitates, theacceleration in the deterioration of a lubricant (base oil and additive)and the increase in the friction or the wear are feared. Accordingly, alubricant which is stable and high in the lubricity even under thesevere conditions encountered when using an ammonia refrigerant, isdemanded.

With respect to the polyether compound, polyether compound derivatives(hereinafter referred to as a polyether compound including thederivatives) where the terminal hydroxyl group thereof is substituted byan alkyl group or an acyl group to improve the stability and themoisture absorption, have been proposed. However, this method hasdisadvantages that a production process for obtaining the derivativesneeds to be added and the good compatibility with ammonia deteriorates.On the other hand, the level of the improvement in the stability and themoisture absorption is not fully satisfactory. Thus, the use of a baseoil comprising such a polyether compound alone is inadequate for solvingthe problem mentioned above. Therefore, it is required that a suitableadditive is selected and used in the combination of ammonia and a baseoil. However, the additive has in many cases higher activity than a baseoil and it also easily reacts with ammonia. Therefore, the deteriorationof the additive and the generation of precipitates are often induced.

The object of the present invention is to provide a lubricant havingexcellent compatibility with ammonia and moreover having excellentpractical performance such as good stability and lubricity, as alubricant for a refrigerator using ammonia as the refrigerant.

DISCLOSURE OF THE INVENTION

As a result of extensive studies, the present inventors have found thatthe above-described problems can be overcome by using as a lubricantbase oil a polyether compound, particularly those having high ratio ofsecondary hydroxyl groups relative to all the hydroxyl groups located atthe structural terminals, and further by adding thereto an additiveselected from an antioxidant, an anti-wear additive and a metaldeactivator.

According to the present invention, the following are provided based onthis finding.

1. A lubricant for a refrigerator using ammonia as the refrigerant,characterized in that the lubricant contains: at least one kind ofadditives selected from antioxidant, anti-wear additive, and metaldeactivator; and at least one polyether compound represented by thefollowing general formula (1) or (2):X {—O—(AO)_(n)—H}_(p)  (1)[wherein X represents a residue resulting from removing a hydroxyl groupfrom a monool or a polyol, (AO)_(n) represents a polyoxy alkylene chainconstituted by copolymerization of an ethylene oxide and an alkyleneoxide having 3 or more carbon atoms, n represents a number of 2 or more,p represents the valence of X, and the number of secondary hydroxylgroups from among hydroxyl groups located at the structural terminal is50% or more of the total number of the hydroxyl groups]X{—O—(AO¹)_(a)—(AO²)_(b)—H}_(p)  (2)[wherein X represents a residue resulting from removing a hydroxyl groupfrom a monool or a polyol, (AO¹)_(a) represents a polyoxyalkylene chainconstituted by copolymerization of an ethylene oxide and an propyleneoxide and/or a butylene oxide, AO²represents an oxyalkylene group having3 or more carbon atoms, a represents a number of 2 or more, b representsa number of 1 or more, and p represents the valence of X].

2. The lubricant for a refrigerator according to the above 1,characterized in that the antioxidant is an aromatic amine compound or aphenothiazine compound.

3. The lubricant for a refrigerator according to the above 1 or 2,characterized in that the metal deactivator is a benzotriazole compound.

4. The lubricant for a refrigerator according to any one of the above 1to 3, characterized in that the anti-wear additive contains at least onekind of compounds selected from the group consisting of a fatty higheralcohol having 10 or more carbon atoms, a polyalcohol partial ester anda polyalcohol partial ether.

5. The lubricant for a refrigerator according to any one of the above 1to 4, characterized in that one of: (AO)_(n) in the general formula (1);and (AO¹)_(a) in the general formula (2) is a polyoxyalkylene groupconstituted by any one of a random copolymer, a block copolymer, and amixed copolymer of a random copolymerization and a blockcopolymerization, between ethylene oxide and propylene oxide and/orbutylene oxide.

6. The lubricant for a refrigerator according to any one of the above 1to 5, characterized in that the kinematic viscosity at 40° C. of thepolyether compound represented by the general formula (1) or (2) is from15 to 200 mm²/s.

7. The lubricant for a refrigerator according to any one of the above 1to 6, characterized in that the ratio of the oxyethylene group in oneof: (AO)_(n) in the general formula (1); and (AO¹)_(a) in the generalformula (2) is from 10 to 50% by mass.

8. The lubricant for a refrigerator according to any one of the above 1to 7, characterized in that the unsaturation degree of the polyethercompound represented by the general formula (1) or (2) is 0.05 meq/g orless.

BEST MODE FOR CARRYING OUT THE INVENTION

A polyether compound used in the present invention is employed as aso-called base oil which is a main constituent of a lubricant, and isrepresented by the following general formula (1) or (2):X{—O—(AO)_(n)—H}_(p)  (1)[wherein X represents a residue resulting from removing a hydroxyl groupfrom a monool or a polyol, (AO)_(n) represents a polyoxy alkylene chainconstituted by copolymerization of an ethylene oxide and an alkyleneoxide having 3 or more carbon atoms, n represents a number of 2 or more,p represents the valence of X, and the number of the secondary hydroxylgroups from among hydroxyl groups located at the structural terminal is50% or more of the total number of the hydroxyl groups].X{—O—(AO¹)_(a)—(AO²)_(b)—H}_(p)  (2)[wherein X represents a residue resulting from removing a hydroxyl groupfrom a monool or a polyol, (AO¹)_(a) represents a polyoxyalkylene groupconstituted by copolymerization of an ethylene oxide and an propyleneoxide and/or a butylene oxide, AO²represents an oxyalkylene group having3 or more carbon atoms, a represents a number of 2 or more, b representsa number of 1 or more, and p represents the valence of X].

In the general formula (1) or (2), X represents a residue resulting fromremoving a hydroxyl group from a monool or a polyol. Examples of themonool include: alcohols such as methanol, ethanol, propanol,2-propanol, butanol, 2-butanol, pentanol, 2-pentanol, 3-pentanol,isopentyl alcohol, 2-methyl-4-pentanol, hexanol, secondary hexanol,isohexanol, heptanol, secondary heptanol, octanol, 2-ethylhexanol,secondary octanol, isooctanol, nonanol, secondary nonanol, 1-decanol,isodecyl alcohol, secondary decanol, undecanol, secondary undecanol,2-methyl decanol, lauryl alcohol, secondary dodecanol, 1-tridecanol,isotridecyl alcohol, secondary tridecanol, myristyl alcohol, secondarytetradecanol, pentadecanol, secondary pentadecanol, cetyl alcohol,palmityl alcohol, secondary hexadecanol, heptadecanol, secondaryheptadecanol, stearyl alcohol, isostearyl alcohol, secondary octadecylalcohol, oleyl alcohol, behenyl alcohol, eicosanol, docosanol,tetracosanol, hexacosanol, octacosanol, myricyl alcohol, laccerol,tetratriacontanol, allyl alcohol, cyclopentanol, cyclohexanol,2-butyloctanol, 2-butyldecanol, 2-hexyloctanol, 2-hexyldecanol,2-hexyldodecanol, 2-octyldecanol, 2-octyldodecanol, 2-octyltetradecanol,2-decyldodecanol, 2-decyltetradecanol, 2-decylhexadecanol,2-dodecyltetradecanol,2-dodecylhexadecanol, 2-dodecyloctadecanol,2-tetradecyloctadecanol, 2-tetradecylicosanol, 2-hexadecyloctadecanoland 2-hexadecylicosanol; and phenols such as phenol, cresol,ethylphenol, tert-butylphenol, hexylphenol, octylphenol, nonylphenol,decylphenol, undecylphenol, dodecylphenol, tridecylphenol,tetradecylphenol, phenylphenol, benzylphenol, styrenated phenol andp-cumylphenol.

Examples of the polyol include: diols such as ethylene glycol, propyleneglycol, 1,4-butanediol, 1,2-butanediol, neopentyl glycol, 1,6-hexandiol,1,2-octanediol, 1,8-octanediol, isoprene glycol,3-methyl-1,5-pentanediol, sorbite, catechol, resorcin, hydroquinone,bisphenol A, bisphenol F, hydrogenated bisphenol A, hydrogenatedbisphenol F and dimerdiol; trihydric alcohol such as glycerol,trioxyisobutane, 1,2,3-butanetriol, 1,2,3-pentanetriol,2-methyl-1,2,3-propanetriol, 2-methyl-2,3,4-butanetriol,2-ethyl-1,2,3-butanetriol, 2,3,4-pentanetriol, 2,3,4-hexanetriol,4-propyl-3,4,5-heptanetriol, 2,4-dimethyl-2,3,4-pentanetriol,pentamethylglycerol, pentaglycerol, 1,2,4-butanetriol,1,2,4-pentanetriol, trimethylolethane and trimethylolpropane;tetrahydric alcohol such as pentaerythritol, erythritol,1,2,3,4-pentanetetrol, 2,3,4,5-hexanetetrol, 1,2,4,5-pentanetetrol,1,3,4,5-hexanetetrol, diglycerol and sorbitan; pentahydric alcohol suchas adonitol, arabitol, xylitol and triglycerol; hexahydric alcohol suchas dipentaerythritol, sorbitol, mannitol, iditol, inositol, darcitol,talose and allose; octahydric alcohol such as saccharose; polyglycerolor the dehydrated condensate thereof. p is a valence of X and ispreferably a number from 1 to 8.

X may be a residue of a compound derived from the above-described monoolor polyol. Examples of such a compound derived from the monool or thepolyol include a sodium alcoholate or a potassium alcoholate of themonool or the polyol above.

Here, if the valence p of X is too large, the polyether compoundobtained may have excessively large molecular weight and excessivelyhigh viscosity or may have reduced compatibility with an ammoniarefrigerant. Therefore, the valence p of X is more preferably from 1 to3. In particular, it is most preferable that p is 1, more specifically,X is a residue resulting from removing a hydroxyl group from a monool.Even in the case of monool, if the number of carbon atoms becomesexcessively large, the polyether compound obtained may have reducedcompatibility with an ammonia refrigerant and therefore, the carbon atomnumber of X is preferably from 1 to 8, more preferably from 1 to 4 and Xis most preferably a methyl group.

In the general formula (1), (AO)_(n) represents a polyoxyalkylene groupconstituted by the copolymerization of an ethylene oxide and an alkyleneoxide having 3 or more carbon atoms. Examples of the alkylene oxidehaving 3 or more carbon atoms include propylene oxide, butylene oxide,α-olefin oxide and styrene oxide. The polymerization ratio of anethylene oxide and an alkylene oxide having 3 or more carbon atoms isnot particularly limited. However, at least the ethylene oxide isnecessary in order to impart excellent compatibility with ammonia to apolyether compound which is a polymerization product.

In formula (2), (AO¹)_(a) represents a polyoxyalkylene group constitutedby the copolymerization of an ethylene oxide and a propylene oxideand/or a butylene oxide. The polymerization ratio of an ethylene oxideand a propylene oxide and/or a butylene oxide is not particularlylimited. However, at least the ethylene oxide is necessary in order toimpart excellent compatibility with ammonia to a polyether compoundwhich is a polymerization product.

However, if the ratio of ethylene oxide is excessively high, themoisture absorption or the low-temperature properties such as the pourpoint may deteriorate, or a powder form solid may separate orprecipitate. Therefore, the ratio of the oxyethylene group in (AO)_(n)or (AO¹)_(a) is preferably 50% by weight or less, more preferably from50 to 5% by weight, most preferably from 30 to 5% by weight. For thesame reason, the ratio of the oxyethylene group in the molecule of thepolyether compound for use in the present invention, which isrepresented by the above-described general formula (1) or (2), ispreferably 40% or less, more preferably 30% or less, and most preferably20% or less based on the molecular weight of the polyether compound.

The form of the copolymerization may be the block polymerization, therandom polymerization or a mixture of the block polymerization and therandom polymerization. However, if the whole part of (AO)_(n) or(AO¹)_(a) are a polyoxy alkylene chain constituted by the blockpolymerization, the fluidity at a low temperature may deteriorate. Thus,it is particularly preferable that the (AO)_(n) or the (AO¹)_(a) is apolyoxy alkylene chain constituted by the random polymerization or it isa polyoxy alkylene chain partially including the random polymerization.n and a each represents a number of 2 or more, preferably 2 to 150, andmore preferably 5 to 100.

The AO² in the general formula (2) represents an oxyalkylene grouphaving 3 or more carbon atoms. Examples of the oxyalkylene group having3 or more carbon atoms include an oxypropylene group, an oxybutylenegroup and an oxyalkylene group having from about 5 to 24 carbon atoms.Among these, an oxypropylene group or an oxybutylene group ispreferable. b represents a number of 1 or more, preferably from 1 to 10.The (AO²)_(b) represents a (poly)oxyalkylene group comprising theabove-described one or more oxyalkylene groups having 3 or more carbonatoms.

The lubricant of the present invention comprises a polyether compoundwhich is represented by the general formula (1) satisfying theabove-described conditions and in which the structural terminal on theopposite side of X is a hydroxyl group. In the polyether compoundrepresented by the general formula (1) for use in the present invention,the number of the secondary hydroxyl groups, of all the hydroxyl groupslocated at the structural terminal, must be 50% or more of the totalnumber of the hydroxyl groups. Further, it is more preferably 70% ormore, and most preferably 80% or more. The reason is that if thesecondary hydroxyl groups comprise 50% or more of all the hydroxylgroups located at the structural terminal, the polyether compoundexhibits excellent stability with respect to an ammonia refrigerant,whereas if the secondary hydroxyl groups comprise less than 50% of thehydroxyl groups located at the structural terminal, the polyethercompound exhibits inferior stability with respect to an ammoniarefrigerant. The secondary hydroxyl group as used herein is a hydroxylgroup bonding to the secondary carbon atom and the ratio of thissecondary hydroxyl group can be measured by ¹H-NMR.

In the polyether compound represented by the general formula (1) for usein the present invention, 50% or more of all the hydroxyl groups locatedat the structural terminal are the secondary hydroxyl groups, andtherefore the polyether compound exhibits excellent stability withrespect to an ammonia refrigerant. The polyether compound represented bythe general formula (2) for use in the present invention has a grouprepresented by (AO²)_(b)—H at the structural terminal and thereforeexhibits excellent stability in the presence of an ammonia refrigerant.

In general, a hydroxyl group bonding to the primary carbon atom changesinto a carboxylic acid through an aldehyde if it is oxidized. However,there is a fear that a carboxylic acid produces an acid amide in thepresence of ammonia and, as a result, the acid amide is precipitated. Incomparison therewith, the hydroxyl group bonding to the secondary carbonatom only changes into a ketone even if it is oxidized and the ketone isstable in the presence of ammonia as compared with a carboxylic acid.Accordingly, it is presumed that the polyether compound used in thepresent invention can exhibit an excellent stability even in thepresence of ammonia because: in the case of the polyether compoundrepresented by the general formula (1), 50% or more of all the hydroxylgroups at the structural terminal bond to the secondary carbon atoms;and in the case of the polyether compound represented by the generalformula (2), it is a polyether compound obtained by finally adding analkylene oxide having 3 or more carbon atoms and in which the hydroxylgroup at the structural terminal bonds to the secondary carbon atom.That is, the lubricant of the present invention solves a problempeculiar to a lubricant for a refrigerator using an ammonia refrigerantby selecting a lubricant having a specific structure as described above.

In the lubricant for a refrigerator using an ammonia refrigerant of thepresent invention, any of the polyether compounds represented by theabove-described general formula (1) and (2) can be used. However, it ismore preferable to use the polyether compound where the secondaryhydroxyl groups from among the hydroxyl groups located at the structuralterminal comprise 50% or more of all the hydroxyl groups and which has astructure represented by the above-described general formula (2).

The molecular weight of the polyether compound represented by thegeneral formula (1) or (2) for use in the present invention is notparticularly limited. However, since the molecular weight has a tendencyto be proportionate to the kinematic viscosity and therefore, themolecular weight is preferably on the order of from 300 to 3,000 inorder to keep the kinematic viscosity within the preferable range asdescribed below.

The kinematic viscosity of the polyether compound represented by thegeneral formula (1) or (2) for use in the present invention is notparticularly limited. However, if the kinematic viscosity is too low,the sealability is poor and the lubricity may also decrease, whereas ifthe kinematic viscosity is too high, the compatibility with ammonia islowered and the energy efficiency also deteriorates. Accordingly, thekinematic viscosity at 40° C. is preferably from 15 to 200 mm²/s, morepreferably from 20 to 150 mm²/s.

From the viewpoint of the cooling ability of a refrigerant and thesealability of a lubricant, the ammonia as a refrigerant and thepolyether lubricant represented by the general formula (1) or (2) of thepresent invention are preferably used at a ratio of from 99/1 to 1/99,more preferably from 95/5 to 30/70 in terms of the mass ratio.

Since the polyether compound represented by the general formula (1) or(2) for use in the present invention is a lubricant used in arefrigerator using an ammonia refrigerant, it is preferable thatimpurities such as moisture or chlorine are present in an amount assmall as possible. Since the moisture accelerates the deterioration ofthe lubricant or additive, it is preferred that its content be as smallas possible, preferably 500 ppm or less, more preferably 300 ppm or lessand most preferably 100 ppm or less. Since a polyether compoundgenerally has a moisture absorption property, the storage or the fillingthereof in a refrigerator requires much care. However, the water can beremoved by the distillation under reduced pressure or using a drierfilled with a desiccant.

In the presence of ammonia, chlorine forms an ammonium salt to cause theblocking of capillary and therefore, the chlorine content is preferablyas small as possible, preferably 100 ppm or less, and more preferably 50ppm or less.

Further, during the production of the refrigerator lubricant of thepresent invention containing an oxypropylene group, propylene oxide maycause a side reaction to produce an allyl group having a carbon-carbondouble bond. If an allyl group is produced, at first, the thermalstability of the lubricant itself decreases. Moreover, a polymerizationproduct is produced to cause sludge and a peroxide is produced becausethe allyl group is easily oxidized. If a peroxide is produced anddecomposed to produce a carbonyl group, the carbonyl group reacts withan ammonia refrigerant to produce an acid amide, so that the acid amidealso causes blocking of capillary. Accordingly, the degree ofunsaturation due to an allyl group or the like is preferably as low aspossible. Specifically, this unsaturation degree is preferably 0.05meq/g or less, more preferably 0.03 meq/g or less and most preferably0.02 meq/g or less.

The peroxide value is preferably 10.0 meq/kg or less, more preferably5.0 meq/kg or less and most preferably 1.0 meq/kg or less. The carbonylvalue is preferably 100 ppm by weight or less, more preferably 50 ppm byweight or less and most preferably 20 ppm by weight or less.

In order to produce such a polyether compound having a low unsaturationdegree represented by the general formula (1) or (2), a reactiontemperature in the case of reacting a propylene oxide is preferably 120°C. or lower, more preferably 110° C. or lower. During the production ofa polyether compound, if an alkali catalyst is used and, in order toremove this, an inorganic-base adsorbent such as activated carbon,activated clay, bentonite, dolomite or aluminosilicate is used, theunsaturation degree can be reduced. When producing or using thelubricant of the present invention, minimizing the contact of thelubricant with oxygen or using an antioxidant at the same time may alsoprevent the increase in the peroxide value or the carbonyl value.

The unsaturation degree, the peroxide value and the carbonyl value asdescribed herein are the values measured by the following methodaccording to Standard Methods for the Analysis of Oils established byJapan Oil Chemists' Soceity. The outline of the measurement methods isdescribed below.

<Measurement Method of Unsaturation Degree (meq/g)>

A sample is reacted with Wijs' solution (IC1-acetic acid solution), leftstanding at a dark place and then, the excess IC1 is reduced to iodine,the iodine content is titrated by sodium thiosulfate to calculate theiodine number, and this iodine number converted into a vinyl equivalentamount and the value thus obtained is defined as the unsaturationdegree.

<Measurement Method of Peroxide Value (meq/kg)>

Potassium iodide is added to a sample, a free iodine produced istitrated with sodium thiosulfate, and this free iodide is converted intoa milliequivalent number based on 1 kg of the sample and the valueobtained is defined as a peroxide value.

<Measurement Method of Carbonyl Value (ppm by Weight)>

2,4-dinitrophenylhydrazine is acted on a sample to produce chromophoricalkynoid ions, and the absorbance of this sample at a wavelength of 480nm is measured. Then, the absorbance thus obtained is converted into thecarbonyl amount based on the analytical curve previously obtained byusing cinnamaldehyde as a standard reference material.

A production method of the polyether compound represented by the generalformula (1) for use in the present invention is not particularly limitedand a usual production method of a polyether compound may be used. Forexample, the polyether may be produced by a method where a mixedalkylene oxide of an ethylene oxide and an alkylene oxide having 3 ormore carbon atoms (e.g. propylene oxide) is reacted with an alcohol suchas methanol as a starting material at a temperature of 100 to 150° C.and under a pressure of about 0 to 10 kg/cm², in the presence of analkali catalyst such as sodium hydroxide or potassium hydroxide.

The polyether compound represented by the general formula (2) may beproduced, for example, by a method where a mixed alkylene oxide of anethylene oxide and a propylene oxide (or butylene oxide) is reacted withan alcohol such as methanol as a starting material under the sameconditions as described above and then an alkylene oxide having 3 ormore carbon atoms such as propylene oxide is reacted therewith. Aproduction method of the polyether compound represented by the generalformula (2) is not particularly limited and the polyether compound maybe produced by a method where a mixed alkylene oxide of an ethyleneoxide and a propylene oxide (or butylene oxide) is reacted with analcohol such as methanol as a starting material under the sameconditions as described above and then an alkylene oxide having 3 ormore carbon atoms such as propylene oxide is reacted therewith.

The lubricant of the present invention further contains at least onekind of additives selected from an antioxidant, an anti-wear additiveand a metal deactivator.

As an antioxidant for use in the present invention, an aromaticamine-base, a phenothiazine-base, a phenol-base, a sulfur-base or a zincthiophosphate-base antioxidant can be blended.

Among these, an aromatic amine-base compound or a phenothiazine-basecompound is particularly preferable because it is a compound chemicallynear to ammonia as a refrigerant and therefore, is favored with highaffinity and excellent compatibility with an ammonia.

Specific examples of the aromatic amine-base compound or thephenothiazine-base compound include dipyridyl amine, phenothiazine,phenothiazine derivatives obtained by adding an alkyl group to aphenylene group, dialkyldiphenylaminedipheyl-p-phenylenediamine,diphenyl-p-phenylenediamine derivatives obtained by substituting aphenyl group with a naphthyl group or an alkyl group anddialkylphenyl-p-phenylenediamine. Among these, preferred are dipyridylamine, p,p′-dialkyldiphenylamine having an alkyl group with 4 to 20carbon atoms (more preferably 4 to 12 carbon atoms, most preferably 8carbon atoms) and N,N′-dialkylphenyl-p-phenylenediamine having an alkylgroup with 2 to 20 carbon atoms (more preferably 4 to 12 carbon atoms).

The added amount of the antioxidant is preferably from 0.01 to 5.0% bymass, more preferably from 0.05 to 1.0% by mass based on the wholeamount of the lubricant for a refrigerator of the present invention. Ifthe added amount is small, an effect as an antioxidant cannot beobtained, whereas an addition amount thereof exceeding 5.0% by mass doesnot bring corresponding improvement of the effect and is thereforeuneconomical. Further, an oil has a tendency to be colored if theantioxidant is excessively added. Therefore, also from this point, anexcessive addition of the antioxidant should be avoided.

Representative examples of the metal deactivator for use in the presentinvention include benzotriazole-base compound and/or the derivativesthereof. The benzotriazole derivative as said herein is a compoundrepresented by the following formula (3):

[wherein R₁, R₂ and R₃, which may be the same or different, each ishydrogen, an alkyl group having from 1 to 20 carbon atoms or an arylgroup having from 1 to 20 carbon atoms]. It is presumed that thesecompounds have a function of covering the metal surface to protect themetal material from corrosive substances such as ammonia refrigerant orthe like.

In the lubricant for a refrigerator of the present invention, the addedamount of the metal deactivator is not particularly limited and may beappropriately selected according to the circumstance, however, it ispreferably from 1 to 200 ppm by mass, more preferably from 5 to 50 ppmby mass based on the entire amount of the lubricant.

Examples of the anti-wear additive for use in the present inventioninclude phosphate-base compound such as tricresyl phosphate andtriphenyl phosphate, alcohol-base compound such as fatty higher alcohol,polyalcohol ester or polyalcohol ether or N-hydrocarbylalkanolamine. Inparticular, the anti-wear additive preferably contains at least one kindof compounds selected from the group consisting of fatty higher alcoholhaving 10 or more carbon atoms, polyalcohol partial ester andpolyalcohol partial ether.

Herein, examples of the fatty higher alcohol having 10 or more carbonatoms include fatty alcohol such as 1-decanol, isodecyl alcohol,secondary decanol, undecanol, secondary undecanol, 2-methyldecanol,laurylalcohol, secondary dodecanol, 1-tridecanol, isotridecyl alcohol,secondary tridecanol, myristyl alcohol, secondary tetradecanol,pentadecanol, secondary pentadecanol, cetyl alcohol, palmityl alcohol,secondary hexadecanol, heptadecanol, secondary heptadecanol, stearylalcohol, isostearyl alcohol, secondary octadecyl alcohol, oleyl alcohol,behenyl alcohol, eicosanol, docosanol, tetracosanol, hexacosanol,octacosanol, myricyl alcohol, laccerol, tetratriacontanol, allylalcohol, cyclopentanol, cyclohexanol, 2-butyloctanol, 2-butyldecanol,2-hexyloctanol, 2-hexyldecanol, 2-hexyldodecanol, 2-octyldecanol,2-octyldodecanol, 2-octyltetradecanol, 2-decyldodecanol,2-decyltetradecanol, 2-decylhexadecanol,2-dodecyltetradecanol,2-dodecylhexadecanol, 2-dodecyloctadecanol,2-tetradecyloctadecanol, 2-tetradecylicosanol, 2-hexadecyloctadecanoland 2-hexadecylicosanol.

The polyalcohol partial ester is a compound represented by the followinggeneral formula (4):R₄(OH)_(h){OC(O)R₅}_(k)  (4)[wherein R₄represents a linear or branched, saturated or unsaturatedhydrocarbon group having from 2 to 12 carbon atoms corresponding to theresidue of polyalcohol having (h+k) valence, R₅ represents a linear orbranched, saturated or unsaturated hydrocarbon group having from 3 to 20carbon atoms, h represents the number of hydroxyl group which is notesterified and remains, k represents the number of acyl groupesterified, and h and k each is a positive number satisfying 1≦h<6,1≦k<6and 2≦h+k≦6]. More specifically, the polyalcohol partial ether is apartial ether obtained by reacting a polyalcohol such as glycol,glycerol, trimethylolpropane, pentaerythritol, sorbitan or sorbitol witha linear or branched, saturated or unsaturated fatty acid having from 3to 20 carbon atoms. Among these, preferred is a partial ether obtainedby reacting a polyalcohol such as glycerol, sorbitan or sorbitol with afatty acid having from 10 to 20 carbon atoms, more preferred is amonofatty acid ester, most preferred is a monofatty acid ester ofglycerol.

The polyalcohol partial ether is a compound represented by the followinggeneral formula (5):R₆(OH)_(r){OR₇}_(s)  (5)[wherein R₆ represents a linear or branched, saturated or unsaturatedhydrocarbon group having from 2 to 12 carbon atoms corresponding to theresidue of polyalcohol having (r+s) valence, R₇ represents a linear orbranched, saturated or unsaturated hydrocarbon group having from 3 to 20carbon atoms, r represents the number of hydroxyl group which is notetherified and remains, s represents the number of ether linkageetherified, and r and s each is a positive number satisfying 1≦r<6,1≦s<6 and 2≦r+s≦6]. More specifically, the polyalcohol partial ether isa partial ether obtained by condensing a polyalcohol such as glycol,glycerol, trimethylolpropane, pentaerythritol, sorbitan or sorbitol witha linear or branched, saturated or unsaturated monool having from 3 to20 carbon atoms. Among these, preferred is a partial ether obtained bycondensing a polyalcohol such as glycerol, sorbitan or sorbitol with afatty alcohol having from 10 to 20 carbon atoms, more preferred ismonoalkyl or alkenyl ether, most preferred is monoalkyl or alkenyl etherof glycerol.

Examples of the N-hydrocarbylalkanolamine include long chainalkylalkanolamines such as N-butyl monoethanolamine, N-hexylmonoethanolamine, N-cyclohexyl monoethanolamine, N-octylmonoethanolamine, N-decyl monoethanolamine, N-coconut oil alkylmonoethanolamine, N-tallow derivation alkyl monoethanolamine, N-soybeanoil derivation alkyl monoethanolamine, N-oleyl monoethanolamine,N-stearyl monoethanolamine, N-butyl diethanolamine, N-hexyldiethanolamine, N-cyclohexyl diethanolamine, N-octyl diethanolamine,N-decyl diethanolamine, N-coconut oil alkyl diethanolamine, N-tallowderivation alkyl diethanolamine, N-soybean oil derivation alkyldiethanolamine, N-oleyl diethanolamine, N-stearyl diethanolamine,N,N-dibutyl monoethanolamine, N,N-dihexyl monoethanolamine,N,N-dicyclohexyl monoethanolamine, N,N-dioctyl monoethanolamine,N,N-didecyl monoethanolamine, N,N-bis (coconut oil derivation alkyl)monoethanolamine, N,N-bis (tallow derivation alkyl) monoethanolamine,N,N-bis (soybean oil derivation alkyl) monoethanolamine, N,N-dioleylmonoethanolamine and N,N-distearyl monoethanolamine or the alkyleneoxide adducts thereof.

In the lubricant for a refrigerator of the present invention, the addedamount of the anti-wear additive is not particularly limited and may beappropriately selected according to the circumstances, however, it ispreferably from 0.1 to 2.0% by mass, more preferably from 0.2 to 1.0% bymass based on the entire amount of the lubricant.

The lubricant for a refrigerator of the present invention contains atleast one kind of additives selected from the above-describedantioxidant, anti-wear additive and metal deactivator. Needless to say,the present invention also includes the case of using an antioxidant, ananti-wear additive and a metal deactivator at the same time. Thelubricant for a refrigerator of the present invention more preferablycontains an additive constituted by using at least one kind of compoundsselected from each of the above-described antioxidant, anti-wearadditive and metal deactivator respectively.

Further, in the lubricant for a refrigerator of the present invention,for example, a commonly known refrigerator lubricant base oil such asnaphthenic mineral oil or synthetic oil such as alkylbenzene oil, etheroil, ester oil, and fluorine or other commonly known additives may beappropriately blend, if desired.

Examples of other commonly known additives include a stabilization agentsuch as phenylglycidyl ether and alkylglycidyl ether, a defoaming agentor a foam suppressor such as polydimethyl siloxane and polymethacrylate.A defoaming agent or a foam suppressor other than the above-describedones, a detergent-dispersant, a viscosity index improver, a corrosioninhibitor and a pour point depressant can be blended, if desired. Theseadditives are usually blended so as to be incorporated in an amount ofabout 10 ppm by mass to 10% by mass in the lubricant of the presentinvention.

A refrigerant used together with the lubricant for a refrigerator of thepresent invention is an ammonia refrigerant; however, the ammoniarefrigerant should be understood as a refrigerant containing ammonia.More specifically, of course, a two-kind mixed refrigerant comprisingammonia and a hydrocarbon compound having a low molecular weight orammonia and the above-described fluorohydrocarbon, and a three-kindmixed refrigerant comprising ammonia, a fluorohydrocarbon compoundhaving a low molecular weight and the above-described fluorohydrocarbonalso correspond to the ammonia refrigerant used in the presentinvention, to say nothing about a refrigerant only comprising ammonia.

The lubricant for a refrigerator of the present invention and an ammoniarefrigerant may be filled at an appropriate ratio according to thespecification of the refrigeration system applied. More specifically,these are filled preferably at a ratio of 99/1 to 1/99, more preferablyat a ratio of 95/5 to 30/70 in terms of the mass ratio of ammoniarefrigerant/lubricant for refrigerator.

EXAMPLES

The present invention is described in greater detail below referring toExamples, but the present invention is not limited to Examples. InExamples, the % expresses % by mass, the ratio expresses mass ratio.

Examples 1 to 12 and Comparative Examples 1 to 10

As a base oil of a lubricant for refrigerator, the following five kindsof polyether compounds were used. To these base oils, the followingantioxidant (two kinds), metal deactivator (one kind) and anti-wearadditive (three kinds) each was added as an additive in an added amountshown in Table 1 and mixed to prepare the lubricant compositions assample oils, which are subjected to the evaluation tests respectively,in Examples and Comparative Examples. These sample oils were subjectedto the evaluation tests of the stability by the sealed tube test, thelubricity by the Falex seizure load and the compatibility with anammonia refrigerant.

<Base Oil>

PAG1: CH₃O (PO)_(m)/(EO)_(n) H

-   -   m/n=8/2, kinematic viscosity (40° C.)=46 mm²/s    -   terminal secondary hydroxyl group ratio: 90%    -   molecular weight: 1,000

PAG2: CH₃O (PO)_(m)/(EO)_(n) H

-   -   m/n=7/3, kinematic viscosity (40° C.)=46 MM²/S    -   terminal secondary hydroxyl group ratio: 60%    -   molecular weight: 1,040

PAG3: CH₃O (PO)_(m)/(EO)_(n) H

-   -   m/n=6/4, kinematic viscosity (40° C.)=46 mm²/s    -   terminal secondary hydroxyl group ratio: 40%    -   molecular weight: 1,060

PAG4: CH₃O (PO)_(m)/(EO)_(n) CH₃

-   -   m/n=8/2, kinematic viscosity (40° C.)=46 mm²/s    -   molecular weight: 1,000

PAG5: CH₃O (PO)_(m) H

-   -   kinematic viscosity (40° C.)=50 mm²/s    -   molecular weight: 950

PAG6: CH₃O (PO)_(m)/(EO)_(n)—(PO)₂—H

-   -   m/n=6/4, kinematic viscosity (40° C.)=54 mm²/S    -   terminal secondary hydroxyl group ratio: 90%    -   molecular weight: 1,170        [wherein PO represents an oxypropylene group, EO represents an        oxyethylene group. (PO)/(EO) represents a random addition of PO        and EO.]

PAG 1 and PAG 2 are included in the polyether compound represented bythe general formula (1) or (2) in the present invention and PAG 6 isincluded in the polyether compound represented by the general formula(2) in the present invention. However, PAG 3 is a base oil where theratio of terminal secondary hydroxyl group is less than 50% based on thewhole hydroxyl group, PAG 4 is a base oil where the both terminalsthereof are blocked up by methyl groups, PAG 5 is a base oil notcontaining an oxyethylene group and all of them are not included in thepresent invention.

<Additive>

(i) Antioxidant (Two Kinds)

DOPA: p,p′-di-octyl-di-phenylamine

DBPC: 2,6-di-tertiary butyl-p-cresol

(ii) Metal Deactivator (One Kind)

BTA: benzotriazole

(iii) Anti-Wear Additive (Three Kinds)

GMOE: glycerol monooleyl ether

GMO: glycerol monoolate

TCP: tricresyl phosphate

TABLE 1 Additives Base Added amount Metal Added amount Anti-wear Addedamount material Antioxidant (% by mass) deactivator (ppm by mass)additive (ppm by mass) Example 1 PAG 1 DOPA 0.05 — — — — Example 2 PAG 1DOPA 0.1  — — — — Example 3 PAG 2 DOPA 0.05 — — — — Example 4 PAG 1 DOPA0.05 BTA 10 — — Example 5 PAG 1 DOPA 0.05 BTA 20 — — Example 6 PAG 1DOPA 0.05 — — GMOE 0.5 Example 7 PAG 1 DOPA 0.05 — — GMOE 1.0 Example 8PAG 1 DOPA 0.05 — — GMO 0.5 Example 9 PAG 2 DOPA 0.05 — — GMOE 0.5Example 10 PAG 1 DOPA 0.05 BTA 10 GMOE 0.5 Example 11 PAG 2 DOPA 0.05BTA 10 GMOE 0.5 Example 12 PAG 6 DOPA 0.05 BTA 10 GMOE 0.5 ComparativePAG 1 — — — — — — Example 1 Comparative PAG 2 — — — — — — Example 2Comparative PAG 6 — — — — — — Example 3 Comparative PAG 3 DBPC 0.1  — —— — Example 4 Comparative PAG 3 — — — — TCP 0.5 Example 5 ComparativePAG 3 DOPA 0.05 BTA 10 GMOE 0.5 Example 6 Comparative PAG 4 — — — — — —Example 7 Comparative PAG 4 DOPA 0.05 BTA 10 GMOE 0.5 Example 8Comparative PAG 5 — — — — — — Example 9 Comparative PAG 5 DOPA 0.05 BTA10 GMOE 0.5 Example 10<Performance Evaluation Test of Lubricant>(i) Stability Test (Sealed Tube Test)

In accordance with JIS K 2211, a sealed tube was manufactured by filling8 ml of each sample oil in Examples and Comparative Examples shown inTable 1 and 2 ml of ammonia refrigerant (R717) to a bomb together withiron and an aluminum catalyst. These sealed tubes were heated and keptat 150° C. for 14 days and then, the appearance of these sample oils andcatalysts thus deteriorated was observed with eyes and evaluated. Theevaluation was based on five-scale evaluation such that if theappearance of sample oils and catalysts after the deterioration was thesame as the one in the beginning, it was evaluated as “no change” and ifa deposit was observed in a sample oil and a discoloration was observedin a catalyst, the sample oil and the catalyst where the degree of suchchange was most serious were evaluated as “deposit 5” and “discoloration5” respectively.

In accordance with JISK2580 ASTM color test method, a color of eachsample oil after the deterioration was measured. More specifically, thecolor of the sample oil was compared with the color of ASTM colorstandard glass and the results thereof were expressed by values inincrements of 0.5 within the range of from 0.5 to 8.0. When the sampleoil color is judged to be from 1.0 to 1.5, a darker color in thestandard glass (in this case, it is 1.5) is adopted and the sample oilcolor is expressed as [L1.5] by attaching L.

(ii) Lubricity Test (Falex Seizure Load Test)

In accordance with ASTM D2670, a steel (AISIC-1137)-made block and asteel (SAE 3135)-made pin were used to apply a load an initialtemperature of 40° C. and a rotating speed of 290 rpm, and the load atthe time of seizure was measured.

(iii) Compatibility Test (Measurement of Two-layer SeparationTemperature)

In accordance with JIS K2211 appendix 3, the two-layer separationtemperature in the mixture of a sample oil/R717 (ammoniarefrigerant)=2/8 was measured.

The results of these evaluation tests are shown in Table 2. The “Fediscoloration” in the catalyst appearance evaluation results of thesealed tube test expresses that a discoloration at the level as shown inTable 2 was observed on the iron in the catalyst, but that adiscoloration was not observed on the aluminum.

TABLE 2 Sealed tube Test Color Appearance of Appearance of Falex seizureTwo-layer separation (ASTM) sample oil catalyst load (N) temperature (°C.) Example 1 L0.5 No change Fe Discoloration 2 3825 −9 Example 2 L1.0No change Fe Discoloration 1 3781 −9 Example 3 L1.5 No change FeDiscoloration 2 4003 −16 Example 4 L0.5 No change No change 3870 −9Example 5 L0.5 No change No change 3914 −9 Example 6 L0.5 No change FeDiscoloration 1 4137 −7 Example 7 L1.0 No change Fe Discoloration 1 4226−6 Example 8 L0.5 No change Fe Discoloration 2 4048 −7 Example 9 L0.5 Nochange Fe Discoloration 2 4359 −14 Example 10 L1.0 No change No change4181 −7 Example 11 L1.5 No change No change 4404 −13 Example 12 L0.5 Nochange Fe Discoloration 1 4137 −16 Comparative L2.5 Deposit 5 FeDiscoloration 5 3736 −9 Example 1 Comparative L3.0 Deposit 5 FeDiscoloration 4 3914 −16 Example 2 Comparative L2.0 Deposit 2 FeDiscoloration 4 4003 −16 Example 3 Comparative L3.5 Deposit 4 FeDiscoloration 4 4092 Room Temperature Example 4 Separation ComparativeL4.5 Deposit 5 Fe Discoloration 5 4582 −24 Example 5 Comparative L3.0Deposit 3 Fe Discoloration 2 4448 −22 Example 6 Comparative L1.5 Deposit2 Fe Discoloration 4 3470 11 Example 7 Comparative L0.5 No change Nochange 3736 12 Example 8 Comparative L1.0 Deposit 1 Fe Discoloration 43114 Room Temperature Example 9 Separation Comparative L0.5 No change Nochange 3336 Example 10

According to Table 2, in the sample oils (Examples 1 to 3) having addedthereto an aromatic amine-base compound or phenothiazine-base compoundas an antioxidant, a discoloration is observed on the appearance of thecatalysts in sealed tube test but is of a tolerable level. The sampleoils (Examples 4 and 5) having added thereto benzotriazole as a metaldeactivator, and the sample oils (Examples 6 to 9) having added theretoglycerol monooleyl ether or glycerol monooleate as an anti-wearadditive, in addition to the aromatic amine compound or thephenothiazine compound, are all improved in their performance such asstability and lubricity than oils in Examples 1 to 3. The sample oils(Examples 10 to 12) having added thereto an aromatic amine compound or aphenothiazine compound, or benzotriazole and glycerol monooleyl etherhave further improved performance. All oils have sufficientcompatibility with an ammonia refrigerant.

On the other hand, the sample oils in Comparative Examples 1 to 3, whichare composed of a PAG1, PAG2 or PAG6 alone without an additive addedthereto, are extremely poor in terms of the appearance of the sampleoils and the catalysts as tested by the sealed tube test, as comparedwith the sample oils in Examples.

The sample oils in Comparative Examples 4 to 6 are obtained by adding anadditive to PAG 3 not included in the present invention. These sampleoils also have poor sealed tube test results and have a problem in thestability as compared with the sample oils in Examples.

The sample oils in Comparative Examples 7 to 10 comprise PAG4 or PAG5alone, which is not included in the present invention, or are sampleoils obtained by adding an additive to the PAG4 or the PAG5. Thesesample oils have a poor compatibility with an ammonia refrigerant andhave a problem in the lubricity.

Industrial Applicability

The present invention is a refrigerator lubricant using a specificpolyether compound as a base oil and containing at least one kind ofadditives selected from antioxidant, anti-wear additive and metaldeactivator, which exhibits a remarkable effect that the performancesuch as stability and lubricity as well as compatibility with ammonia isextremely improved, and is useful as a lubricant for a refrigeratorusing an ammonia refrigerant.

1. A lubricant for a refrigerator using ammonia as the refrigerant,characterized in that the lubricant contains: at least one kind ofadditive selected from antioxidant, anti-wear additive, and metaldeactivator; and at least one polyether compound having an unsaturationdegree of 0.05 meg/or less represented by the following general formula(1) or (2):X{—O—(AO)_(n)—H}_(p)  (1)X{—O—(AO¹)_(a)—(AO²)_(b)—H}_(p)  (2)
 2. The lubricant for a refrigeratoraccording to the above 1, characterized in that the antioxidant is anaromatic amine compound or a phenothiazine compound.
 3. The lubricantfor a refrigerator according to claim 1, characterized in that the metaldeactivator is a benzotriazole compound.
 4. The lubricant for arefrigerator according to claim 1, characterized in that the anti-wearadditive contains at least one kind of compounds selected from the groupconsisting of a fatty higher alcohol having 10 or more carbon atoms, apolyalcohol partial ester and a polyalcohol partial ether.
 5. Thelubricant for a refrigerator according to claim 1, characterized in thatone of: (AO)_(n) in the general formula (1); and (AO¹)_(a) in thegeneral formula (2) is a polyoxyalkylene group constituted by any one ofa random copolymer, a block copolymer, and a mixed copolymer of a randomcopolymerization and a block copolymerization, between ethylene oxideand propylene oxide and/or butylene oxide.
 6. The lubricant for arefrigerator according to claim 1, characterized in that the kinematicviscosity at 40° C. of the polyether compound represented by the generalformula (1) or (2) is from 15 to 200 mm²/s.
 7. The lubricant for arefrigerator according to claim 1, characterized in that the ratio ofthe oxyethylene group in one of: (AO)_(n) in the general formula (1);and (AO¹)_(a) in the general formula (2) is from 5 to 50% by mass.